Vehicles are typically provided with suspension systems that isolate the sprung mass, i.e. the components supported by the suspension system, from the unsprung mass, including, for example, the suspension system, wheels, and axles. Suspension systems typically include springs and sometimes dampers which act as an interface between the sprung and unsprung masses. The springs and dampers impart a degree of flexibility into the suspension system in order to dampen shock and isolate the sprung mass from vibrations, bumps, and road irregularities that are generated or encountered by the unsprung mass as the vehicle travels.
While the flexible characteristics of suspension systems imparted by the springs and dampers are desirable for purposes of providing a comfortable ride, inclusion of springs and dampers often times has a deleteriously affect on the handling of the vehicle. For example, during cornering or turning, the sprung mass of the vehicle may tilt or roll about the longitudinal axis of the vehicle frame. Whereas it would be desirable to stiffen the suspension system in order to increase the average roll rate of the sprung mass, for example by stiffening the springs, this would have a deleterious effect on the ability of the suspension system to dampen shock and isolate the sprung mass from vibrations, bumps, and road irregularities.
Another way to improve the roll rate is to utilize stabilizer bars. Stabilizer bars are typically mounted to the frame and opposite ends of the axle or opposing suspension control arms connected to opposite ends of the axle. During a roll event, when the sprung mass attempts to roll, the stabilizer bar restrains the rolling motion. As this occurs, torsion is applied to the stabilizer bar, which causes the stabilizer bar to bend and twist. Stabilizer bars are designed to have sufficient torsional resiliency to endure this bending and twisting motion and sufficient torsional stiffness to restrain the rolling motion. Advantageously, stabilizer bars are typically designed and positioned so that any bending and twisting that does occur is translated as a bending and twisting motion about an axis that is generally transverse to the axis about which roll occurs, whereby such bending and twisting does not substantially contribute to vehicle roll.
Yet another way to improve the roll characteristics is to use axles in a manner analogous to stabilizer bars. In particular, suspension control arms may be pivotably connected to the frame, for example, to a frame hanger bracket, via a pivotable joint and rigidly connected to the axle so that relative motion does not occur between the axle and the control arms during non-roll event driving conditions. Accordingly, during non-roll event driving conditions the control arms and axle pivot about the pivotable joint and the fixedly mounted portion of the control arm travels up and down with the axle in response to vibrations, bumps, and road irregularities generated or encountered by the unsprung mass as the vehicle travels.
During a roll event, however, when the sprung mass attempts to roll, the axle restrains the rolling motion. In particular, during a roll event, torsion is applied to the control arm, which, in turn, applies torsion to the axle, which, in turn, causes the axle to bend and twist. Axles used in this manner are designed to have sufficient torsional resiliency to endure this bending and twisting motion and sufficient torsional stiffness to restrain the rolling motion. Advantageously, since the bending and twisting motion is about an axis of the axle, which is generally transverse to the axis about which roll occurs, such bending and twisting does not substantially contribute to vehicle roll. In such a manner the axle may itself increase the roll rate, whether used in conjunction with stabilizer bars to provide auxiliary roll control or whether used in the absence of stabilizer bars. For heavy trailers and vehicles, such as, for example, truck tractors, cement trucks, and dump trucks, in particular, the ability to provide such roll control or auxiliary roll control may prove especially desirable.
As discussed above, previously known systems that employ axle bend and twist to limit sprung mass roll have entailed fixedly connecting the control arms to the axle, rather than pivotably connecting the control arms to the axle. However, relative to four bar link suspension systems, which include control arms pivotably connected to both the frame and the axle, such an arrangement generates deficiencies in certain aspects of vehicle handling. Accordingly, roll control aside, it is generally preferable from a handling standpoint to employ a four bar link type suspension system. As an example, those of ordinary skill in the art will appreciate that four bar link type suspension systems generally provide improved torque reactivity and improved longitudinal location of the axle relative to the frame as the axle moves up and down during non-roll event driving conditions. Previously known four bar link suspension systems have had the drawback, however, in that they have not used axle bend and twist to provide roll control or auxiliary roll control.
For example, U.S. Pat. No. 5,649,719 shows a four bar link arrangement comprising lower control arms pivotably mounted to the frame and the axle and an upper control arm pivotably mounted to the frame and the axle. Despite the desirableness of using an axle for roll control or auxiliary roll control, for a variety of reasons, arrangements such as that shown in U.S. Pat. No. 5,649,719 and a variety of other types of four bar linkage suspension systems have heretofore proved incapable of generating axle bend and twist to provide roll control.
The present invention is directed toward a vehicle with a four bar link suspension system provided with improved roll characteristics.